As is well known, in addition to red cells and white cells, blood contains various components such as glucose, albumin, calcium and the like. Methods for measuring concentrations of these components include an optical method and an electrochemical method. Specifically, a sample (blood) as an analyte is applied to a pad (which is generally worked into an elongated test piece) retaining a reagent, and the resulting reaction is analyzed optically or electrochemically. In the optical method, a portion of the reagent pad which exhibits color reaction is irradiated with light, and the light reflected thereon or the light passing therethrough is analyzed. In the electrochemical method, electrochemical change during the oxidation/reduction reaction occurring in the reagent pad is analyzed with electrodes. Through such analysis, the concentration of a particular component in the blood is determined.
Whichever one of the optical method and the electrochemical method is utilized, to measure the concentration of a component other than blood cells (i.e. blood plasma) while avoiding measurement errors, it is preferable to separate blood plasma from blood cells in advance. Generally, for this purpose, a centrifugal separator is used.
Conventionally, various analyzers incorporating centrifugal separators are proposed for automatically measuring the concentration of a component in blood. An example of such analyzers is disclosed in JP-A-61 (1986)-13158. As shown in FIG. 11 of the accompanying drawings of the present application, the disclosed analyzer (generally indicated by reference number 8) includes a centrifugal separator 9, a pipette unit 80, a constant-temperature bath 81 and an optical measuring unit (not shown).
As shown in FIG. 12, the centrifugal separator 9 includes three rotary discs 90 equally spaced from each other along a hypothetical circumference. The discs 90 are fixed to a rotation shaft 92 via horizontal arms 92. The rotation shaft 92 is rotatable about its axis intermittently at a pitch of 120 degrees. Therefore, each of the discs 90 stopped at one of three stop points A, B and C shown in FIG. 11 moves to a next one of the points.
As shown in FIG. 12, each of the rotary discs 90 is circumferentially provided with a plurality of holes 93 equally spaced from each other. As shown in FIG. 13, a cylindrical container 95 for holding a test tube 94 is pivotally provided in each of the holes 93.
As shown in FIG. 11, the analyzer 8 has an upper surface 82 formed with an opening 83 which is generally equal in diameter to the discs 90, thereby exposing the upper surface of the disc 90 (90a) positioning at the first stop point A. Therefore, the test tubes 94 (FIG. 12) can be easily inserted into the cylindrical containers 95 (FIG. 13) in the discs 90.
After test tubes are inserted into all of the cylindrical containers 95 of the disc 90a, the rotation shaft 91 (FIG. 12) is rotated through 120° to move the disc 90a to the second stop point B. At this point, the disc 90a is rotated at a speed of no less than 3000 rpm to centrifugally separate the sample.
Subsequently, the rotation shaft 91 (FIG. 12) is further rotated through 120° to move the disc 90a to the third point C. The upper surface 82 of the analyzer 8 is formed, at the stop point C, with a pipette insertion hole 84 of a relatively small diameter. At the stop point C, an intended one of the test tubes 94 supported by the disc 90a can be located directly below the pipette insertion hole 84 by intermittently rotating the disc 90a. Thus, supernatant liquid (blood plasma) is taken from each of the test tubes 94 through the pipette insertion hole 84.
The blood plasma thus taken is spotted, through a spotting hole 85, to reagent pads of test pieces (not shown) set in the constant-temperature bath 81. The color reaction occurring at each of the reagent pads is analyzed by the above-described optical method.
Although the above-described prior art analyzer 8 functions properly in many ways, it has the following problems.
Generally; the number of test tubes 94 to be set to the centrifugal separator 9 is not always the same but may vary at each time of the operations for centrifugal separation. Specifically, in one case, all of the cylindrical containers 95 may be loaded with test tubes 94 (containing samples), but in another case, the number of test tubes 94 to be set may be smaller than the number of cylindrical containers 95. In the former case, the center of gravity of the three rotary discs 90 (and the test tubes 94 containing samples) coincides with the axis of the rotation shaft 92. However, in the latter case, the center of gravity of the three rotary discs 90 (and the test tubes 94 containing samples) does not coincide with the axis of the rotation shaft 92. Therefore, the axis deflection of the rotation shaft 92 is likely to occur during the operation, which increases the possibility of the failure of the centrifugal separator 9.
Conventionally, to avoid such a trouble, measures need be taken for keeping the rotation balance of the centrifugal separator when the number of the test tubes 94 containing samples is smaller than the maximum capacity. Specifically, the test tubes 94 need be so set in each rotary disc as to be far from each other as much as possible or a dummy test tube or tubes as a counterbalance need be used.
However, such works are troublesome and considerably deteriorate the efficiency of the sample analysis. Particularly, in a small-scale hospital which has only one or two doctors, it is not advantageous to use the above-described analyzer 8. This is because, generally in such a small-scale hospital, it is not usual to perform blood tests simultaneously with respect to many samples, so that the work for balancing the rotation of the centrifugal separator 9 is almost always necessary. Further, since the prior art analyzer 8 is relatively large, it maybe difficult to find appropriate space for disposing the analyzer in such a small-scale hospital.